Cholinergic supersensitivity of the iris sphincter helps to make the diagnosis of "
tonic pupil." Because uncertain responses sometimes occur with
mecholyl 2.5%, dilute solutions of
pilocarpine are often used. There has always been some question as to whether individual variation in corneal permeability was one of the factors contributing to the variability in pupillary constriction to topical
cholinergics in these patients. In this study, the degree of intraocular penetration of topical
fluorescein was compared with the degree of
pilocarpine-induced
miosis in six
tonic pupils and in seven age-matched normal controls. A noncontact fluorophotometer and a computerized videopupillogram were used. The patients showed a significant
cholinergic supersensitivity in their affected
tonic pupils and had normal intraocular penetration of
fluorescein through the cornea in both eyes. It is concluded that the
cholinergic supersensitivity of the iris in
tonic pupils is not the result of increased corneal permeability but instead results from an increased sensitivity of the
cholinergic receptors in iris sphincter muscles.